In a common load supply system, as backup power of the system, a battery realizes that a load continues to function properly in the case of a main power supply source failure, which ensures the stable and reliable operation of the system. Overcurrent protection for a battery is implemented by cascading an overcurrent protector at a battery input port. When the battery is overly charged/discharged, or the temperature thereof is too high, the overcurrent protector can disconnect automatically so as to protect a load equipment and the battery. The state of the overcurrent protector for the battery is of vital importance, which describes the charging/discharging state of the battery and reflects whether the overcurrent protector is damaged and connected. In the load supply system, the location of the overcurrent protector for battery protection in the whole system is shown in FIG. 1, wherein the system includes a main power supply, the overcurrent protector, the battery, the load and the like.
In general, there are two methods for deciding a state of an overcurrent protector. One is to decide the state of the overcurrent protector according to a state of an auxiliary contact of the overcurrent protector. As shown in FIG. 2, disconnection of the overcurrent protector will lead to jump of the auxiliary contact of the overcurrent protector, the jump of the auxiliary contact is detected via a hardware circuit, thus deciding the state of the overcurrent protector; the other is to decide the state of the overcurrent protector for the battery according to a voltage difference between a battery voltage and a system voltage, namely, voltage difference across the overcurrent protector for the battery. As shown in FIG. 3, when the overcurrent protector is disconnected (OFF), the battery voltage and the system voltage are not the same, the voltage difference across the overcurrent protector is compared, and then the voltage difference is converted to a numerical quantity, via which the state of the overcurrent protector is decided.
The detecting method to decide the state of the overcurrent protector according to the state of the auxiliary contact of the overcurrent protector has the following disadvantages: in general, the auxiliary contact adopts a mechanical transmission, which will often lead to the ineffectiveness of the auxiliary contact, thereby making the detection unreliable; compared with the overcurrent protector without the auxiliary contact, the overcurrent protector with the auxiliary contact is higher in price, and has no advantage in terms of costs; and the method requires that a system monitoring equipment must have a hardware detecting circuit for the auxiliary contact, which increases monitoring hardware costs.
The method for deciding the state of the overcurrent protector for the battery according to the voltage difference between the battery voltage and the system voltage has the following disadvantages: the voltage difference between the battery voltage and the system voltage is associated with the quality and extent of charging/discharging of the battery, when the quality of the battery is good and the extent of charging/discharging is low, this voltage difference will be very small. And the voltage difference decision will usually be based on one fixed criterion, in the case of a low voltage difference across the overcurrent protector, this will thus inevitably lead to the misjudgement of the state of the overcurrent protector. In addition, the method requires that a DC power monitoring equipment must have a voltage interface circuit and a voltage comparing and distinguishing circuit, which increases monitoring hardware costs.